Many superior characteristics of white light-emitting diodes (LEDs) such as high efficiency, low energy-consumption, long lifetime, and excellent reliability have been promoting their penetration into the market for large size flat panel backlighting, street lighting, and museum and residential illuminations. The most commonly used method to generate white light is combining a semiconductor chip emitting at a short wavelength (blue, violet or ultraviolet) with a wavelength converting phosphor which absorbs a portion of light emitted from the diode and undergoes secondary emission at a longer wavelength. Conventional phosphors are composed of an inorganic host substance, such as yttrium aluminum garnet (YAG), containing an optically active dopant which is usually one of the rare-earth elements or a rare-earth compound. The application of the inorganic phosphors is often limited by the resource depletion of rare-earth elements, difficulty in color tuning, and non-uniform dispersion within polymer resins. Typically, inorganic phosphors are mixed in the form of powders with resin, and scattering leads to significantly reduced optical efficiency.
Thus, in order to improve the performance of high brightness white LEDs in terms of higher luminous efficiency and better color rendering ability, highly transparent and efficient light conversion materials are urgently needed.
While certain aspects of conventional technologies have been discussed to facilitate disclosure of the invention, Applicants in no way disclaim these technical aspects, and it is contemplated that the claimed invention may encompass one or more of the conventional technical aspects discussed herein.
In this specification, where a document, act or item of knowledge is referred to or discussed, this reference or discussion is not an admission that the document, act or item of knowledge or any combination thereof was, at the priority date, publicly available, known to the public, part of common general knowledge, or otherwise constitutes prior art under the applicable statutory provisions; or is known to be relevant to an attempt to solve any problem with which this specification is concerned.